001    /*
002     * Copyright (C) 2007 The Guava Authors
003     *
004     * Licensed under the Apache License, Version 2.0 (the "License");
005     * you may not use this file except in compliance with the License.
006     * You may obtain a copy of the License at
007     *
008     * http://www.apache.org/licenses/LICENSE-2.0
009     *
010     * Unless required by applicable law or agreed to in writing, software
011     * distributed under the License is distributed on an "AS IS" BASIS,
012     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013     * See the License for the specific language governing permissions and
014     * limitations under the License.
015     */
016    
017    package com.google.common.collect;
018    
019    import com.google.common.annotations.GwtCompatible;
020    import com.google.common.annotations.GwtIncompatible;
021    
022    import java.io.IOException;
023    import java.io.ObjectInputStream;
024    import java.io.ObjectOutputStream;
025    import java.util.LinkedHashMap;
026    
027    /**
028     * A {@code Multiset} implementation with predictable iteration order. Its
029     * iterator orders elements according to when the first occurrence of the
030     * element was added. When the multiset contains multiple instances of an
031     * element, those instances are consecutive in the iteration order. If all
032     * occurrences of an element are removed, after which that element is added to
033     * the multiset, the element will appear at the end of the iteration.
034     * 
035     * <p>See the Guava User Guide article on <a href=
036     * "http://code.google.com/p/guava-libraries/wiki/NewCollectionTypesExplained#Multiset">
037     * {@code Multiset}</a>.
038     *
039     * @author Kevin Bourrillion
040     * @author Jared Levy
041     * @since 2.0 (imported from Google Collections Library)
042     */
043    @GwtCompatible(serializable = true, emulated = true)
044    @SuppressWarnings("serial") // we're overriding default serialization
045    public final class LinkedHashMultiset<E> extends AbstractMapBasedMultiset<E> {
046    
047      /**
048       * Creates a new, empty {@code LinkedHashMultiset} using the default initial
049       * capacity.
050       */
051      public static <E> LinkedHashMultiset<E> create() {
052        return new LinkedHashMultiset<E>();
053      }
054    
055      /**
056       * Creates a new, empty {@code LinkedHashMultiset} with the specified expected
057       * number of distinct elements.
058       *
059       * @param distinctElements the expected number of distinct elements
060       * @throws IllegalArgumentException if {@code distinctElements} is negative
061       */
062      public static <E> LinkedHashMultiset<E> create(int distinctElements) {
063        return new LinkedHashMultiset<E>(distinctElements);
064      }
065    
066      /**
067       * Creates a new {@code LinkedHashMultiset} containing the specified elements.
068       *
069       * <p>This implementation is highly efficient when {@code elements} is itself
070       * a {@link Multiset}.
071       *
072       * @param elements the elements that the multiset should contain
073       */
074      public static <E> LinkedHashMultiset<E> create(
075          Iterable<? extends E> elements) {
076        LinkedHashMultiset<E> multiset =
077            create(Multisets.inferDistinctElements(elements));
078        Iterables.addAll(multiset, elements);
079        return multiset;
080      }
081    
082      private LinkedHashMultiset() {
083        super(new LinkedHashMap<E, Count>());
084      }
085    
086      private LinkedHashMultiset(int distinctElements) {
087        // Could use newLinkedHashMapWithExpectedSize() if it existed
088        super(new LinkedHashMap<E, Count>(Maps.capacity(distinctElements)));
089      }
090    
091      /**
092       * @serialData the number of distinct elements, the first element, its count,
093       *     the second element, its count, and so on
094       */
095      @GwtIncompatible("java.io.ObjectOutputStream")
096      private void writeObject(ObjectOutputStream stream) throws IOException {
097        stream.defaultWriteObject();
098        Serialization.writeMultiset(this, stream);
099      }
100    
101      @GwtIncompatible("java.io.ObjectInputStream")
102      private void readObject(ObjectInputStream stream)
103          throws IOException, ClassNotFoundException {
104        stream.defaultReadObject();
105        int distinctElements = Serialization.readCount(stream);
106        setBackingMap(new LinkedHashMap<E, Count>(
107            Maps.capacity(distinctElements)));
108        Serialization.populateMultiset(this, stream, distinctElements);
109      }
110    
111      @GwtIncompatible("not needed in emulated source")
112      private static final long serialVersionUID = 0;
113    }